I actually tried that this fall; I made 2 and a half attempts LOL -- I wanted them to be snug like a good swaddle but open at the end (with drawstring) for diaper changes ...
The first: not quite stretchy enough, especially with the bind off around the hood (whoops - need to learn the stretchy bind off)
neighbor kid (pictured) loved it once it was on, but it was too much tugging to get it over his head and down, and it couldn't be taken off either way (which might be important in the event of a blowout diaper)
my baby loved it once it was on and the width was much stretchier, but the length/bulky yarn made the whole thing too bulky to easily get baby into - again had to tug the tube up or down (tried it both ways) and baby didn't like to be in the middle on the way ... plus it was hard not to get it on twisted, so baby's face aligned with the hood hole. I ended up frogging the hood, and will probably frog the whole thing, eventually.
The other one (attempt #2, not pictured) was with a thin yarn (DK weight) and was looking more like a nice sweater sleeve, but I decided it wasn't going to have enough circumference ... so I abandoned it for now.
Anyway, just my experience, I have not gotten the "long tube with a drawstring" to work for me, yet.
I'm posting this so maybe someone can learn from my mistakes and improve on the idea, LOL - because both babies DID love being snuggled IN them.